This section is intended to introduce various aspects of the art, which may be associated with exemplary embodiments of the present disclosure. This discussion is believed to assist in providing a framework to facilitate a better understanding of particular aspects of the present disclosure. Accordingly, it should be understood that this section should be read in this light, and not necessarily as admissions of prior art.
Field of the Invention
The present disclosure relates to the field of well completions and downhole operations. More specifically, the present invention relates to a sand control device, and methods for conducting wellbore operations using a fluid filtering device.
Discussion of Technology
In the drilling of oil and gas wells, a wellbore is formed using a drill bit that is urged downwardly at a lower end of a drill string. After drilling to a predetermined depth, the drill string and bit are removed and the wellbore is lined with a string of casing. An annular area is thus formed between the string of casing and the formation. A cementing operation is typically conducted in order to fill or “squeeze” the annular area with cement. The combination of cement and casing strengthens the wellbore and facilitates the isolation of the formation behind the casing.
It is common to place several strings of casing having progressively smaller outer diameters into the wellbore. The process of drilling and then cementing progressively smaller strings of casing is repeated several times until the well has reached total depth. The final string of casing, referred to as a production casing, is cemented in place and perforated. In some instances, the final string of casing is a liner, that is, a string of casing that is not tied back to the surface.
As part of the completion process, a wellhead is installed at the surface. The wellhead controls the flow of production fluids to the surface, or the injection of fluids into the wellbore. Fluid gathering and processing equipment such as pipes, valves and separators are also provided. Production operations may then commence.
In some instances, a wellbore is completed in a formation that is loose or “unconsolidated.” This means that as production fluids are produced into the wellbore, formation particles, e.g., sand and fines, may also invade the wellbore. Such particles are detrimental to production equipment. More specifically, formation particles can be erosive to downhole pumps as well as to pipes, valves, and fluid separation equipment at the surface.
The problem of unconsolidated formations can occur in connection with the completion of a cased wellbore. In that instance, formation particles may invade the perforations created through production casing and a surrounding cement sheath. However, the problem of unconsolidated formations is much more pronounced when a wellbore is formed as an “open hole” completion.
In an open-hole completion, a production casing is not extended through the producing zones and perforated; rather, the producing zones are left uncased, or “open.” A production string or “tubing” is then positioned inside the wellbore extending down below the last string of casing and across a subsurface formation.
There are certain advantages to open-hole completions versus cased-hole completions. First, because open-hole completions have no perforation tunnels, formation fluids can converge on the wellbore radially 360 degrees. This has the benefit of eliminating the additional pressure drop associated with converging radial flow and then linear flow through particle-filled perforation tunnels. The reduced pressure drop associated with an open-hole completion virtually guarantees that it will be more productive than an unstimulated, cased hole in the same formation. Second, open-hole techniques are oftentimes less expensive than cased hole completions. In this respect, an open-hole completion eliminates the need for cementing, perforating, and post-perforation clean-up operations.
A common problem in open-hole completions is the immediate exposure of the wellbore to the surrounding formation. If the formation is unconsolidated or heavily sandy, the flow of production fluids into the wellbore will likely carry with it formation particles, e.g., sand and fines.
To control the invasion of sand and other particles, sand control devices may be employed. Sand control devices are usually installed downhole across formations to retain solid materials larger than a certain diameter while allowing fluids to be produced. A sand control device typically includes an elongated tubular body, known as a base pipe, having numerous slotted openings or perforations. The base pipe is then typically wrapped with a filtration medium such as a well screen, a wire wrap screen, or a metal mesh screen.
To augment sand control devices, particularly in open-hole completions, it is common to install a gravel pack. Gravel packing a well involves placing gravel or other particulate matter around the sand control device after the sand control device is hung or otherwise placed in the wellbore. To install a gravel pack, a particulate material is delivered downhole by means of a carrier fluid. The carrier fluid with the gravel together form a gravel slurry. The slurry dries in place, leaving a circumferential packing of gravel. The gravel not only aids in particle filtration but also helps maintain wellbore integrity.
It is also known in the oil and gas industry to deploy stand-alone screens. These screens are placed into the wellbore at the end of a production string. Generally, it is more cost effective to install a stand-alone sand screen than a gravel pack. However, stand-alone screens tend to be less robust than a gravel pack. The single sand control barrier in a stand-alone screen exposed to an initially open wellbore annulus is more susceptible to erosion damage during well production.
In either instance, sand screens are sometimes installed across highly pressurized formations. These formations may be subject to rapid erosion. When a screen is installed in, for example, a high-pressure, high-productivity formation having high permeability streaks, a sand screen can be particularly vulnerable to failure. A sand screen may also be locally plugged by residual mud or produced formation sand, leaving a “hot spot” for produced fluids. Such hot spots are prone to sand erosion. Further, sand screens can be damaged during run-in.
In order to strengthen the sand screen and to protect it from the so-called “hot spots,” the MazeFlo™ sand control system has been previously developed. A patent was granted for this technology in 2008 as U.S. Pat. No. 7,464,752. In one embodiment, the technology offers a pair of concentric filtering tubular bodies that are dimensioned to be placed in a wellbore along a producing formation.
The tubular bodies include a first perforated base pipe. The first base pipe provides a first fluid flow path within a wellbore. At least one section of the first perforated base pipe is impermeable to fluids, while at least one section of the first perforated base pipe is permeable to fluids. The permeable section is adapted to retain particles larger than a predetermined size while allowing fluids to pass through the permeable section.
The tubular bodies also include a second perforated base pipe inside. The second base pipe provides a second fluid flow path within a wellbore. At least one section of the second perforated base pipe is impermeable to fluids, while at least one section of the second perforated base pipe is permeable to fluids. The permeable section is adapted to retain particles larger than a predetermined size while allowing fluids to pass through the permeable section.
The at least one permeable section of the first base pipe is in fluid communication with at least one permeable section of the second base pipe. In this way, fluid communication is provided between the first flow path and the second flow path. However, it is preferred that the at least one permeable section of the first base pipe be staggered from the at least one permeable section of the second base pipe.
The MazeFlo™ sand control system offers redundancy for a downhole screen. In this way, if an outer screen fails at any point, sand particles will still be filtered by an inner screen. The staggered design between the outer screen and inner screen streamlines any sand-laden flow and significantly reduces the erosion risk on the inner screen. U.S. Pat. No. 7,464,752 is incorporated herein in its entirety by reference.
Despite the success of the MazeFlo™ sand control system, a need exists for further technical developments in this area. Specifically, a need exists for an improved fluid filtering tool that may be used for either hydrocarbon production or fluid injection during a wellbore operation, and that provides redundancy in the filtering media.